1. Field of the Invention
The invention relates to a silencing apparatus for a vehicle, which includes a muffler having a flattened sectional shape in which the width is greater than the height, an inlet pipe through which exhaust gas flows into an inside of the muffler, an outlet pipe through which the exhaust gas flows out of the inside of the muffler, a partition plate that divides the inside of the muffler into sound-deadening chambers, and a communication hole that extends through the partition plate.
2. Description of Related Art
As a silencing apparatus for a vehicle, there is a muffler provided in an exhaust system of an internal combustion engine. The muffler disposed beneath the floor of a vehicle generally has a flattened sectional shape in which the width is greater than the height, for example, an elliptical sectional shape, en elongated circular sectional shape, etc., for the sake of mountability.
A muffler having a flattened sectional shape that has a width W as shown in FIG. 13A will be considered. In this muffler, air column resonance occurs in the width direction thereof, with two opposite ends of the muffler in the width direction thereof being closed ends. The air column resonance lowers the sound deadening performance of the muffler. The wavelength λ of a standing wave that causes air column resonance in the muffler in the width direction thereof is “2W/n (n is an integer equal to or greater than 1)”. If the sonic velocity is represented by “C (≈20×vT where T is the gas temperature within the muffler)”, the frequency f of the air column resonance is represented as “C×m/2W (m is an integer equal to or greater than 1)”. In this air column resonance, the standing waves that most conspicuously appear are two standing waves, that is, a standing wave whose wavelength λ is twice the muffler width (λ=2W) as shown in FIG. 13B, and a standing wave whose wavelength λ is equal to the muffler width (λ=W) as shown in FIG. 13C.
In related art, as a countermeasure against high-frequency exhaust sound as in the air column resonance in the width direction of a muffler, a sub-muffler that has a high-frequency resonance structure or that is filled with a sound absorbing material is provided in the exhaust system, as in Japanese Patent Application Publication No. 2009-062922 (JP-A-2009-062922).
If the sub-muffler is appropriately designed, it is certainly possible to restrain increase of the exhaust sound that results from the air column resonances in the width direction of the muffler. However, if the sub-muffler is installed, corresponding increases in cost and mass are inevitable. Therefore, it is demanded to provide a vehicle silencing apparatus that effectively restrains the increase of exhaust sound caused by the air column resonances in the muffler width direction at a reduced cost.